Journal of Molecular Structure 1076 (2014) 475–482

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Journal of Molecular Structure

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Zinc(II) and Cadmium(II) complexes with N4-coordinate pyrazole basedligand: Syntheses, characterization and structure

http://dx.doi.org/10.1016/j.molstruc.2014.07.0820022-2860/� 2014 Elsevier B.V. All rights reserved.

⇑ Corresponding author.

Ankita Solanki a, Mehul H. Sadhu a, Sujit Baran Kumar a,⇑, Partho Mitra b

a Department of Chemistry, Faculty of Science, The Maharaja Sayajirao University of Baroda, Vadodara 390 002, Indiab Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, 2A and 2B Raja S.C. Mullick Road, Jadavpur, Kolkata 700032, India

h i g h l i g h t s

� Synthesis and characterization of ninemononuclear Zn(II) and Cd(II)complexes with ligand dbdmp andpseudohalides.� Synthesis and characterization of two

binuclear cadmium(II) complexeswith N3

� ion.� Structures of [Zn(N3)(dbdmp)]ClO4

and [Cd(NCO)(dbdmp)]ClO4

complexes with tbp geometry.� Structure of [{Cd(dbdmp)}2(l-

N3)2](ClO4)2 and [Cd(NCS)2(dbdmp)]with octahedral geometry.

g r a p h i c a l a b s t r a c t

A series of nine new mononuclear zinc(II) and cadmium(II) complexes and two binuclear cadmium(II)complexes have been synthesized by using ligand dbdmp and pseudohalogens and characterized byphysico-chemical methods. Crystal structures of the complexes [Zn(N3)(dbdmp)]ClO4 (1),[{Cd(dbdmp)}2(l-N3)2](ClO4)2 (7), [Cd(NCO)(dbdmp)]ClO4 (9) and [Cd(NCS)2(dbdmp)] (11) have beensolved by single crystal X-ray diffraction studies.

a r t i c l e i n f o

Article history:Received 24 May 2014Received in revised form 11 July 2014Accepted 31 July 2014Available online 7 August 2014

Keywords:Zinc(II) and cadmium(II) complexesTetradentate ligandPseudohalidesNew crystal structures

a b s t r a c t

A series of six new mononuclear zinc(II) complexes of the type [Zn(X)(dbdmp)]Y (1–6) (X = N3�/NCO�/

NCS�, Y = ClO4�/PF6

�, and dbdmp = N,N-diethyl-N0 ,N0-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)ethane-1,2-diamine), two binuclear cadmium(II) complexes [{Cd(dbdmp)}2(l-N3)2](Y)2 (7–8) and three mononu-clear cadmium(II) complexes [Cd(NCO)(dbdmp)]Y (Y = ClO4

�/PF6�) (9–10) and [Cd(NCS)2(dbdmp)] (11)

have been synthesized and characterized by physico-chemical methods. Crystal structures of the com-plexes [Zn(N3)(dbdmp)]ClO4 (1), [{Cd(dbdmp)}2(l-N3)2](ClO4)2 (7), [Cd(NCO)(dbdmp)]ClO4 (9) and[Cd(NCS)2(dbdmp)] (11) have been solved by single crystal X-ray diffraction studies and showed that[Zn(N3)(dbdmp)]ClO4 (1) and [Cd(NCO)(dbdmp)]ClO4 (9) have distorted trigonal bipyramidal geometry,[Cd(NCS)2(dbdmp)] (11) and [(dbdmp)Cd(l-N3)]2(ClO4)2 (7) have distorted octahedral geometry.

� 2014 Elsevier B.V. All rights reserved.

Introduction

Transition metal complexes containing bridging ligands likeazide, thiocyanate and isocyanate are very interesting because oftheir various modes of coordination and formation of mono,

N

C

X

M

X

C

N

M

N N NM M

NNN

N C XM M

NCX

X = O, S

M M

XCN

NCX

N

N

N

M

N C X

M M

(I) (II) (III) (IV) (V) (VI) (VII)

M M

NNN

NNN

(VIII)

Scheme 1. Different coordination modes of pseudohalides.

476 A. Solanki et al. / Journal of Molecular Structure 1076 (2014) 475–482

di- and polynuclear complexes [1–7]. Among these bridgingligands, azide and thiocyanate anion are versatile ligands. Theazide ion bridges the metal center either by end-on (l-1,1) orend-to-end (l-1,3) coordination mode whereas the thiocyanateion preferably adopts end-to-end (l-1,3) coordination mode [8–12]. Pseudohalides can also act as monodentate ligand and formmononuclear complex with transition elements (Scheme 1)[13,14]. But it is not possible to know whether they will act asmonodentate or bridging ligand in the bi- and polynuclear com-plexes. Although a large number of mono, bi- and polynuclearcomplexes of copper(II), nickel(II) with azide or thiocyanate orisocyanate have been reported, number of papers on zinc(II) andcadmium(II) complexes with pseudohalides are relatively less[15–22]. Among the pseudohalides containing cadmium com-plexes, the number of isocyanate containing cadmium complexesstructurally characterized is rare.

The synthesis and characterization of zinc (II) and cadmium (II)complexes with pyrazole based ligand are of considerable interestbecause of their potential application in the field of catalysis[23,24], molecular sieves and luminescence materials [25,26]. Zincis an important element in the bio-system and plays an importantrole in the active centers in metalloenzymes. Pyrazole containingligand and their metal complexes also have biological activities[27]. A number of zinc(II) complexes with nitrogen containing het-erocyclic ligand have been synthesized and characterized and theirbiological activity studied [28,29].

As a part of our research on synthesis, characterization and andthe structure determination of transition metal complexes withpseudohalides and pyrazole based ligand, we have reported mono-nuclear and binuclear nickel(II) complexes and mononuclear cop-per(II) complexes with pseudohalides and substituted pyrazolebased ligand [30,31]. In this paper we report on the syntheses,characterization and structures of zinc(II) and cadmium(II) com-plexes with pseudohalies like azide/thiocyanate or isocyanateand tetradentate N4-coordinate pyrazole based ligand N,N-diethyl-N0,N0-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)ethane-1,2-diamine (dbdmp). All zinc(II) complexes and NCS� andNCO� containing cadmium(II) complexes are mononuclear,whereas azide containing cadmium(II) complexes are binuclear.

Experimental

Materials

The chemicals and solvents were of analytical grade and pur-chased from commercial sources. Acetylacetone, paraformalde-hyde, hydrazine hydrate, sodium azide, Zn(CH3COO)2�2H2O(Qualigens, India), Cd(CH3COO)2�2H2O (SRL, India), N,N-diethyleth-ylenediamine, NH4PF6 (Aldrich) were of reagent grade and used asreceived. N,N-diethyl-N0,N0-bis((3,5-dimethyl-1H-pyrazol-1-yl)-methyl)ethane-1,2-diamine (dbdmp) was synthesized accordingto the reported method [31]. M(ClO4)2�6H2O [(M = Zn(II) and

Cd(II)] were prepared by reaction of metal carbonate with diluteHClO4 acid and followed by slow evaporation of the solution.

Instruments

The IR spectrums were recorded on a Perkin–Elmer FT-IR spec-trometer RX1 spectrum using KBr pellets. The micro analysis (C, Hand N) were carried out using a Perkin–Elmer IA 2400 series ele-mental analyzer. UV–Vis spectra (900–190 nm) were recorded ona Perkin-Elmer spectrophotometer model Lambda 35 in acetoni-trile solution. Solution conductivity were measured in CH3CN solu-tion using Equip-Tronics conductivity meter (model No. EQ-660A).

Synthesis of complexes

[Zn(N3)(dbdmp)]ClO4 (1)To a stirring methanol solution (5 ml) of Zn(ClO4)2�6H2O (0.186 g,

0.5 mmol), ligand dbdmp (0.166 g, 0.5 mmol) in methanol (10 ml)was added drop by drop. After 10 min, NaN3 (0.033 g, 0.5 mmol) inwater (1 ml) was added slowly to the mixture. This solution was stir-red for 3 h at room temperature, filtered and kept for slow evapora-tion. Block shaped colorless crystals were obtained after five dayswhich were washed with diethyl ether and dried in vacuo. Yield.0.150 g (56%). Found C = 40.15%, H = 6.05%, N = 23.28%, Anal calcfor C18H32N9O4ClZn: C = 40.08, H = 5.98, N = 23.37%. IR (KBr pellet)cm�1; m(C2H5 + CH3), 2984, 2943 m; m(N3

�), 2079 vs; m(C@ C) + m(C@N)/pz ring, 1551 s, 1466 s; masmy(ClAO), 1106; d(OAClAO), 624s. UV–Vis spectra: kmax/nm (in CH3CN) (emax/mol�1 cm�1) 215(28,048). KM (X�1 cm2 mol�1) = 122.

[Zn(N3)(dbdmp)]PF6 (2)A methanol solution (5 ml) of ligand dbdmp (0.166 g, 0.5 mmol)

was added drop wise to a stirring solution of Zn(CH3COO)2�2H2O(0.110 g, 0.5 mmol) in the same solvent (10 ml). To this NaN3

(0.032 g, 0.5 mmol) in water (1 ml) was added slowly. After10 min NH4PF6 (0.0815 g, 0.5 mmol) in water (1 ml) was addedand the colorless mixture was stirred for 5 h, filtered and kept atroom temperature for slow evaporation. After few days block shapedpale yellow colored crystals were obtained. Yield. 0.180 g (61%).Found C = 36.75%, H = 5.59%, N = 21.96%, Anal calc for C18H32N9PF6

Zn: C = 36.96%, H = 5.51%, N = 21.55%. IR (KBr pellet) cm�1; m(C2

H5 + CH3), 2980, 2952 m; m(N3�), 2088 vs; m(C@C) + m (C@N)/pz ring,

1552 s, 1464 s; m(PF6�), 865 s. UV–Vis spectra: kmax/nm (in CH3CN)

(emax/mol�1 cm�1) 214 (25,836). KM (X�1 cm2 mol�1) = 120.

[Zn(NCO)(dbdmp)]ClO4 (3)This complex was prepared by following the same procedure as

for complex 1 except NaNCO was used instead of NaN3. Colorlesscrystals were obtained after slow evaporation of solvent. Yield.0.200 g (68%). Found C = 42.23%, H = 5.74%, N = 18.35%, Anal calcfor C19H32N7O5ClZn: C = 42.31%, H = 5.78%, N = 18.18%. IR (KBr pel-let) cm�1; m(C2H5 + CH3), 3149, 2924 m; m(NCO�), 2233 vs;

Table 1Crystal parameters of complexes 1, 7, 9 and 11.

[Zn(N3)(dbdmp)]ClO4 (1) [{Cd(dbdmp)}2(l-N3)2](ClO4)2

(7)[Cd(NCO)(dbdmp)]ClO4 (9) [Cd(NCS)2(dbdmp)] (11)

Empirical formula C18H32N9O4ClZn C36H64Cd2Cl2N18O8 C19H32CdN7O5Cl C20H32CdN8S2

Formula weight 539.35 1172.77 586.38 561.09Temperature (K) 295(2) 150.0(10) 293(2) 293(2)Wavelength (Å) 0.71073 1.54184 1.54184 0.71073Crystal system Monoclinic Monoclinic Monoclinic MonoclinicSpace group P21/c P21/c P21/c C2/ca (Å) 8.5154(6) 8.56730(10) 8.6201(2) 34.460(6)b (Å) 19.2104(13) 21.6683(3) 21.9666(7) 8.1191(15)c (Å) 14.4727(10) 12.8970(2) 13.0473(4) 18.700(3)a (�) 90 90 90 90b (�) 91.937(2) 100.106(2) 99.630(3) 99.965(7)c (�) 90 90 90 90Volume (Å3) 2366.2(3) 2357.04(6) 2435.75(12) 5153.0(16)Z 4 2 4 8Density (Mg/m3) 1.514 1.653 1.599 1.446Absorption coefficient

(mm�1)1.195 8.850 8.572 1.033

F(000) 1128 1200 1200 2344Theta range for data

collection (�)1.76–32.25 4.01–71.94 3.98–71.63 1.20–25.24

Index ranges �12 6 h 6 11,�25 6 k 6 27,�20 6 l 6 21

�6 6 h 6 10,�25 6 k 6 26,�15 6 l 6 13

�6 6 h 6 10,�26 6 k 6 25,�16 6 l 6 14

�38 6 h 6 38,�9 6 k 6 9,�20 6 l 6 21

Reflections collected 37,274 8877 9189 20,831Independent reflections 7704 4645 4651 3845

[R(int) = 0.0386] [R(int) = 0.0313] [R(int) = 0.0404] [R(int) = 0.0402]Absorption correction Semi-empirical from equivalents Semi-empirical from

equivalentsSemi-empirical fromequivalents

Semi-empirical fromequivalents

Refinement method Full-matrix least-squares on F2 Full-matrix least-squares on F2 Full-matrix least-squares on F2 Full-matrix least-squares on F2

Data/restraints/parameters 7704/0/304 4645/0/304 4651/0/298 3845/0/280Goodness-of-fit on F2 1.029 1.079 1.171 1.039Final R indices R1 = 0.0324 R1 = 0.0440 R1 = 0.0665 R1 = 0.0312[I > 2sigma(I)] wR2 = 0.0777 wR2 = 0.1276 wR2 = 0.1710 wR2 = 0.0773R indices (all data) R1 = 0.0404 R1 = 0.0461 R1 = 0.0746 R1 = 0.0389

wR2 = 0.0809 wR2 = 0.1304 wR2 = 0.1756 wR2 = 0.0820Largest diff. peak and hole

(e A�3)0.737 and �0.535 2.153 and �1.629 1.344 and �0.933 0.286 and �0.464

A. Solanki et al. / Journal of Molecular Structure 1076 (2014) 475–482 477

m(C@C) + m (C@N)/pz ring, 1528 s, 1423 s; masmy(ClAO), 1088 vs;d(OAClAO), 628 s. UV–Vis spectra: kmax/nm (in CH3CN) (emax/mol�1 cm�1) 219 (27,563). KM (X�1 cm2 mol�1) = 118.

[Zn(NCO)(dbdmp)]PF6 (4)This complex was prepared by following the same procedure as

for complex 2 except NaNCO was used instead of NaN3. Colorlesscrystals were obtained after slow evaporation of solvent. Yield.0.165 g (56%). Found C = 39.23%, H = 5.49%, N = 16.85%, Anal calcfor C19H32N7OF6PZn: C = 39.02%, H = 5.51%, N = 16.76%. IR (KBr pel-let) cm�1; m(C2H5 + CH3), 3123, 2926 m; m(NCO�), 2235 vs;m(C@C) + m (C@N)/pz ring, 1555 s, 1416 s; m(PF6

�), 846 s. UV–Visspectra: kmax/nm (in CH3CN) (emax/mol�1 cm�1) 217 (23,885). KM

(X�1 cm2 mol�1) = 115.

[Zn(NCS)(dbdmp)]ClO4 (5)This complex was prepared by following the same procedure as

for complex 1 except KSCN was used instead of NaN3. Colorlesscrystals were obtained after slow evaporation of solvent. Yield.0.197 g (71%). Found C = 41.23%, H = 5.79%, N = 17.39%, Anal calcfor C19H32N7O4ClSZn: C = 41.09%, H = 5.81%, N = 17.65%. IR (KBrpellet) cm�1; m(C2H5 + CH3), 2980 m; m(NCS�), 2076 vs; m(C@C) + m(C@N)/pz ring, 1552 s, 1468 s; masmy(ClAO), 1089 vs; d(OAClAO),625 s. UV–Vis spectra: kmax/nm (in CH3CN) (emax/mol�1 cm�1)220 (24,763). KM (X�1 cm2 mol�1) = 114.

[Zn(NCS)(dbdmp)]PF6 (6)This complex was prepared by following the same procedure as

for complex 2 except KSCN was used instead of NaN3. Colorlesscrystals were obtained after slow evaporation of solvent. Yield.

0.187 g (63%). Found C = 37.83%, H = 5.40%, N = 16.45%, Anal calcfor C19H32N7SF6PZn: C = 37.98%, H = 5.37%, N = 16.32%. IR (KBr pel-let) cm�1; m(C2H5 + CH3), 3146, 2988 m; m(NCS�), 2066 vs;m(C@C) + m (C@N)/pz ring, 1558, 1468 s; m(PF6

�), 845 s. UV–Visspectra: kmax/nm (in CH3CN) (emax/mol�1 cm�1) 221 (23,989). KM

(X�1 cm2 mol�1) = 117.

[{Cd(dbdmp)}2(l-N3)2](ClO4)2 (7)To a stirring solution of Cd(ClO4)2�6H2O in methanol, ligand

dbdmp (0.166 g, 0.5 mmol) was added into it. After 5 min NaN3

(0.032 g, 0.5 mmol) in water (1 ml) was added. This mixture wasstirred for 4 h then filtered and kept for slow evaporation. Colorlessneedle shaped crystals were obtained after 3 days. Yield. 0.240 g(82%). Found C = 36.76%, H = 5.44%, N = 21.75%, Anal calc forC36H64N18O8Cd2Cl2: C = 36.87%, H = 5.50%, N = 21.50%. IR (KBrpellet) cm�1; m(C2H5 + CH3), 3131, 2972 m; m(N3

�), 2031, 2073 vs;m(C@C) + m (C@N)/pz ring, 1552 s, 1464 s; masmy(ClAO), 1075 vs;d(OAClAO), 624 s. UV–Vis spectra: kmax/nm (in CH3CN)(emax/mol�1 cm�1). 217 (29,973). KM (X�1 cm2 mol�1) = 195.

[{Cd(dbdmp)}2(l-N3)2](PF6)2 (8)Cd(CH3COO)2�2H2O (0.133 g, 0.5 mmol) was dissolved in of

methanol (5 ml) and ligand dbdmp (0.166 g, 0.5 mmol) in methanol(10 ml) was added into it. To this solution, NaN3 (0.032 g, 0.5 mmol)in water (1 ml) was added. After 15 min NH4PF6 (0.82 g, 0.5 mmol)was dissolved in water (1 ml) and added drop by drop. This yellowcolored mixture was stirred for 4 h, filtered and kept for slow evap-oration. White colored needle shaped crystals were obtained after2 days. Yield. 0.198 g (69%). Found C = 34.46%, H = 5.04%,N = 19.83%, Anal calc for C36H64N18F12Cd2P2: C = 34.21%, H = 5.10%,

Table 2Bond lengths (Å) and bond angles (�) of complexes 1, 7, 9 and 11.

[Zn(N3)(dbdmp)]ClO4 (1) [{Cd(dbdmp)}2(l-N3)2](ClO4)2 (7) [Cd(NCO)(dbdmp)]ClO4(9) [Cd(NCS)2(dbdmp)] (11)

Bond length (Å)Zn(1)AN(7) 2.0001(13) Cd(1)AN(1) 2.289(3) Cd(1)AN(1) 2.293(7) Cd(1)AN(7) 2.223(3)Zn(1)AN(5) 2.0517(11) Cd(1)AN(3) 2.453(3) Cd(1)AN(3) 2.445(7) Cd(1)AN(8) 2.315(4)Zn(1)AN(1) 2.0713(12) Cd(1)AN(5) 2.307(3) Cd(1)AN(5) 2.290(7) Cd(1)AN(5) 2.357(3)Zn(1)AN(6) 2.1176(11) Cd(1)AN(6) 2.376(3) Cd(1)AN(6) 2.351(7) Cd(1)AN(1) 2.369(3)Zn(1)AN(3) 2.3046(12) Cd(1)AN(7) 2.222(4) Cd(1)AN(7) 2.157(7) Cd(1)AN(3) 2.483(3)

Cd(1)AN(8) 2.617(4) Cd(1)AN(6) 2.540(3)Cd(1)� � �Cd(1i) 5.4701(4)

[Zn(N3)(dbdmp)]ClO4 (1) [{Cd(dbdmp)}2(l-N3)2](ClO4)2 (7)

Bond angles (�)N(7)AZn(1)AN(5) 107.60(5) N(6)ACd(1)AN(8) 163.24(12)N(1)AZn(1)AN(6) 125.71(4) N(7)ACd(1)AN(3) 172.14(13)N(5)AZn(1)AN(1) 111.43(5) N(1)ACd(1)AN(5) 138.47(12)N(7)AZn(1)AN(3) 175.76(5) N(7)ACd(1)AN(6) 107.59(13)N(5)AZn(1)AN(6) 109.44(4) N(3)ACd(1)AN(8) 86.54(11)N(7)AN(8)AN(9) 176.59(15) N(8)AN(9)AN(7) 176.5(4)

[Cd(NCO)(dbdmp)]ClO4 (9) [Cd(NCS)2(dbdmp)] (11)

N(1)ACd(1)AN(6) 100.1(3) N(7)ACd(1)AN(3) 169.28(12)N(7)ACd(1)AN(3) 169.4(3) N(7)ACd(1)AN(5) 108.10(12)N(5)ACd(1)AN(1) 136.0(2) N(8)ACd(1)AN(6) 163.59(13)N(7)ACd(1)AN(6) 113.2(3) N(1)ACd(1)AN(5) 143.17(11)N(5)ACd(1)AN(6) 96.3(2) N(7)AC(19)AS(1) 176.0(4)N(7)AC(19)AO(5) 178.6(9) N(8)AC(20)AS(2) 175.4(4)

Symmetry code: i = 1 � x, �y, 1 � z.

478 A. Solanki et al. / Journal of Molecular Structure 1076 (2014) 475–482

N = 19.95%. IR (KBr pellet) cm�1;m(C2H5 + CH3), 2986, 2928, 2875 m;m(N3

�), 2093, 2038 vs; m(C@C) + m (C@N)/pz ring, 1556 s, 1469 s;m(PF6

�), 841 s. UV–Vis spectra: kmax/nm (in CH3CN) (emax/mol�1

cm�1) 215 (26,530). KM (X�1 cm2 mol�1) = 210.

[Cd(NCO)(dbdmp)]ClO4 (9)This complex was prepared by following the same procedure as

for complex 7 except NaNCO was used instead of NaN3. Colorlesscrystals were obtained after slow evaporation of solvent. Yield.0.210 g (72%). Found C = 38.86%, H = 5.49%, N = 16.85%, Anal calcfor C19H32N7O5Cd1Cl1: C = 38.92%, H = 5.50%, N = 16.72%. IR (KBrpellet) cm�1; m(C2H5 + CH3), 3132, 2972 m; m(NCO�), 2202 vs;m(C@C) + m (C@N)/pz ring, 1552 s, 1464 s; masmy(ClAO), 1094 vs;d(OAClAO), 624 s. UV–Vis spectra: kmax/nm (in CH3CN) (emax/mol�1 cm�1) 214 (28,937). KM (X�1 cm2 mol �1) = 125.

[Cd(NCO)(dbdmp)]PF6 (10)This complex was prepared by following the same procedure as

for complex 8 except NaNCO was used instead of NaN3. Colorlesscrystals were obtained after slow evaporation of solvent. Yield.0.195 g (62%). Found C = 36.02%, H = 5.12%, N = 15.39%, Anal calcfor C19H32N7O1Cd1P1F6: C = 36.12%, H = 5.10%, N = 15.52%. IR (KBrpellet) cm�1; m(C2H5 + CH3), 2986, 2931 m; m(NCO�), 2227 vs;m(C@C) + m (C@N)/pz ring, 1556 s, 1474, 1469 s; m(PF6

�), 842 s.

NN

N NN

N

Et Et

[(dbdmp)Cd

[Cd(NCO)(d

[Cd(NCS)2(

[Zn(X)(dbdm

dbdmp

Zn(ClO4)2.6H2O

X

M = Zn, CdX = N3

-, NCO-, NCS-

M(CH3COO)2.2H2O

Cd(ClO4)2.6H2O

XMeOH

RT

Scheme 2. Syntheses of Zn(I

UV–Vis spectra: kmax/nm(in CH3CN) (emax/mol�1 cm�1) 216(27,687). KM (X�1 cm2 mol�1) = 122.

[Cd(NCS)2(dbdmp)] (11)This complex was prepared by following the same procedure as

for complex 7 except KSCN was used instead of NaN3. Colorlesscrystals were obtained after slow evaporation of solvent. Yield.0.140 g (49%). Found C = 42.86%, H = 5.70%, N = 19.85%, Anal calcfor C20H32N8S2Cd: C = 42.81%, H = 5.75%, N = 19.97%. IR (KBr pellet)cm�1; m(C2H5 + CH3), 2984, 2868 m; m(NCS�), 2074, 2041 vs;m(C@C) + m (C@N)/pz ring, 1556 s, 1462 s. UV–Vis spectra: kmax/nm (in CH3CN) (emax/mol�1 cm�1) 211 (27,567). KM

(X�1 cm2 mol�1) = 10.

X-ray crystallography

The details of data collection and some important features ofthe refinement for the compounds 1, 7, 9 and 11 are given inTable 1 and selected bond lengths and angles are given in Table 2.Colorless crystals of suitable size of complexes were obtained byslow evaporation of methanol solution. Single crystal X-ray diffrac-tion intensity data of the complexes 1 and 11 were collected at293 K using Bruker APEX-II CCD diffractometer equipped with

(µ-N3)2](ClO4)2

bdmp)]ClO4

dbdmp)]

p)]ClO4

X- PF6-

[Zn(X)(dbdmp)]PF6

[(dbdmp)Cd(µ-N3)2](PF6)2

[Cd(NCO)(dbdmp)]PF6

[Cd(NCS)2(dbdmp)]

I) and Cd(II) complexes.

Fig. 1. ORTEP diagram depicting the cationic part of the [Zn(N3)(dbdmp)]ClO4 (1)complex with atom numbering scheme (30% probability factor for the thermalellipsoids. H-atoms are omitted for the clarity).

Fig. 2. ORTEP diagram depicting the cationic part of the [(dbdmp)Cd(l-N3)]2�(ClO4)2 (7) complex with atom numbering scheme (30% probability factor for thethermal ellipsoids. H-atoms are omitted for the clarity).

Fig. 3. ORTEP diagram depicting the cationic part of the [Cd(NCO)(dbdmp)]ClO4 (9)complex with atom numbering scheme (30% probability factor for the thermalellipsoids. H-atoms are omitted for the clarity).

A. Solanki et al. / Journal of Molecular Structure 1076 (2014) 475–482 479

graphite monochromated Mo-Ka radiation (k = 0.71073 Å) andOxford X-CALIBUR-S CCD diffractometer with Cu-Ka radiation(k = 1.54184 Å) at 150 K for complex 7 and at 293 K for complex9. Data reduction was carried out using the program Bruker SAINT[32] and CrysAlisPro, Agilent Technologies, Version 1.171.35.19. Anabsorption correction based on multi-scan method [33] wasapplied. The structures were solved by direct methods and refinedby the full-matrix least-square technique on F2 using the programsSHELXS-97 and SHELXL-97 [34] respectively. All calculations werecarried out using WinGX system Ver-1.64 [35]. All hydrogen atomswere located from difference Fourier map and treated as riding. Allnon hydrogen atoms were refined with anisotropic displacementcoefficients.

Results and discussion

Synthesis and formulation

The mononuclear complexes of the type [Zn(X)(dbdmp)]Y (1–6)have been synthesized by reacting Zn(ClO4)2�6H2O/Zn(CH3COO)2�

2H2O, tetradentate N4-coordinate ligand dbdmp, X (N3�/NCO�/

NCS�) and Y (ClO4�/PF6

�) ions in 1:1:1:1 mol ratio in the presenceof aqueous methanol at room temperature and isolated as stablecolorless crystals in good yield (Scheme 2). There is no change ofcomposition of the complexes even with excess addition of X ionsin the reaction. The molar conductivity measurement in CH3CNsolution (�10�3 M) shows all the zinc complexes are 1:1 electro-lyte (KM �120 X�1 cm2 mol�1). There was no change of molar con-ductivity even after 2 h indicating no decomposition of thecomplexes in the solution. Furthermore, the presence of counteranion was confirmed by IR spectra and single crystal X-ray diffrac-tion studies of [Zn(N3)(dbdmp)]ClO4 (1) (Fig. 1). All complexes gavesatisfactory microanalysis results confirming their molecular com-position. The complexes are stable in air and moderately soluble inacetonitrile, methanol, ethanol, dichloromethane, acetone, etc.

Mononuclear cadmium(II) complexes [Cd(NCO)(dbdmp)]Y and[Cd(NCS)2(dbdmp)] and binuclear cadmium(II) complexes[{Cd(dbdmp)}2(l-N3)2](Y)2 (Y = ClO4

�/PF6�) were obtained as color-

less compound through one pot reaction of Cd(ClO4)2�6H2O/Cd(CH3COO)2�2H2O, ligand dbdmp, pseudohalides (N3

�/NCO�/NCS�) and PF6

� in 1:1:1:1 mol ratio in presence of aqueous metha-nol at room temperature. IR spectral data shows that azide ion con-taining compounds 7 and 8 are binuclear. This was also confirmedby single crystal X-ray diffraction studies of complex[{Cd(dbdmp)}2(l-N3)2](ClO4)2 (7) (Fig. 2). Isocyanate containingcomplexes 9 and 10 are mononuclear with distorted trigonal bipy-ramidal geometry which is confirmed by single crystal diffractionstudies of the complex [Cd(NCO)(dbdmp)]ClO4 (9) (Fig. 3). The[Cd(NCS)2(dbdmp)] (11) complex is non ionic which is confirmedby conductance measurement (KM �10 X�1 cm2 mol�1), IR spectraand single crystal X-ray diffraction studies. This complex[Cd(NCS)2(dbdmp)] (11) has different molecular composition thancorresponding zinc complexes 5 and 6. The important point is thatexcept two cadmium azide complexes 7 and 8, all zinc and cad-mium complexes 1–6 and 9–11 are mononuclear. The azide con-taining cadmium complexes 7 and 8 are binuclear with doubleend-to-end (l-1,3) coordination mode. The molar conductivitymeasurement in CH3CN solution (�10�3 M) shows the complexes9 and 10 are 1:1 electrolyte (KM �120 X�1 cm2 mol�1) whereascomplexes 7 and 8 are 1:2 electrolyte (KM > 180 X�1 cm2 mol�1)indicating the presence of counter anion in the molecule [36].

Table 3IR spectral data of the complexes 1–11.

Compounds m(C@C) + m(C@N)/pz ring m(N3�)/m(NCO�)/m(NCS�) masmy(ClAO) + d(OAClAO) m(PF6

�)

[Zn(N3)(dbdmp)]ClO4 (1) 1551, 1466 2079 1106, 624 –[Zn(N3)(dbdmp)]PF6 (2) 1552, 1464 2088 – 865[Zn(NCO)(dbdmp)]ClO4 (3) 1528, 1423 2233 1088,628 –[Zn(NCO)(dbdmp)]PF6 (4) 1555, 1416 2235 – 846[Zn(NCS)(dbdmp)]ClO4 (5) 1552, 1468 2076 1089, 625 –[Zn(NCS)(dbdmp)]PF6 (6) 1558, 1468 2066 – 845[{Cd(dbdmp)}2(l-N3)2](ClO4)2 (7) 1552, 1464 2031, 2073 1075, 624 –[(dbdmp)Cd(l-N3)]2(PF6)2 (8) 1556, 1469 2038, 2093 – 841[Cd(NCO)(dbdmp)]ClO4 (9) 1552, 1464 2202 1094, 624 –[Cd(NCO)(dbdmp)]PF6 (10) 1556, 1474 2227 – 842[Cd(NCS)2(dbdmp)] (11) 1556, 1462 2074, 2042 – –

Fig. 4. ORTEP diagram of the complex [Cd(NCS)2(dbdmp)] (11) with atomnumbering scheme (30% probability factor for the thermal ellipsoids. H-atoms areomitted for the clarity).

480 A. Solanki et al. / Journal of Molecular Structure 1076 (2014) 475–482

All complexes gave satisfactory microanalysis results confirmingtheir molecular composition. The diffraction quality crystals forstructural studies were obtained by slow evaporation of the solu-tion. The complexes are stable in air and moderately soluble in ace-tonitrile, methanol, ethanol, dichloromethane, acetone etc.

In the study presented here, the present N4-coordinated tetra-dentate pyrazole containing ligand form penta coordinated mono-nuclear complexes with trigonal bipyramidal geometry and sixcoordinated mono- or binuclear distorted octahedral geometrywith zinc(II) and cadmium(II) in presence of pseudohalides likeazide or thiocyanate or isocyanate. Similar, tetradentate N4-coordi-nated pyridyl-pyrazole based ligand form five coordinated mono-nuclear complexes with trigonal bipyramidal geometry andsix coordinated binuclear complexes with distorted octahedralgeometry with same metal ions and same pseudohalides [37–39].Therefore, we can conclude that pyrazole containing tetradentateN4-coordinated ligand form mononuclear complexes with eithertrigonal bipyramidal (complexes) or distorted octahedral geometryand binuclear distorted octahedral geometry with Zn(II) and Cd(II)ions in the presence of pseudohalides like azide, thiocyanate orisocyanate, although zinc(II) and cadmium (II) prefer to form tetra-hedral complexes [40]. Another important point is that most of thereported azide bridged binuclear cadmium(II) complexes have end-on (l-1,1) coordination mode of bonding [37,41,42] but thecompound [{Cd(dbdmp)}2(l-N3)2](ClO4)2 (7) synthesized by ushave rare end-to-end (l-1,3) coordination mode of bonding.

IR data

The IR spectra of the complexes were assigned in comparison ofthe IR spectra of the ligand. In free ligand, two strong bands arefound at 1555 cm�1 and 1459 cm�1 which are assigned asm(C@C) and m(C@N) bands of pyrazole ring. All the complexes alsoshow two intense bands at �1550 and �1460 cm�1 and these twobands are also present in the ligand indicating the coordination ofligand dbdmp in the metal complexes (Table 3). IR spectra of com-plexes 1–2 exhibited a sharp peak in the region of 2079–2088 cm�1

due to asymmetric stretching vibration of terminal m(N3�) ion. For

complexes 3 and 4, a sharp band appeared at � 2233 cm�1 dueto asymmetric stretching vibration of N-bonded terminal m(NCO�)ion. Two sharp bands in the range 2031–2073 cm�1 for 7 and at2096–2057 cm�1 for 8 indicating the bridging mode of coordina-tion of azide ion in the complexes [43]. One sharp peak at�2220 cm�1 is observed in the IR spectra of complexes 9 and 10indicating the coordination of NCO� ion. An intense band appearedin the region of 2046–2076 cm�1 due to asymmetric stretchingvibration of N-bonded terminal m(NCS�) ion for the complexes 5,6 and 11. The IR spectra of complexes 1, 3, 5, 7 and 9 shows a broadband in the region of 1100 cm�1 and a weak band at 625 cm�1 con-firm the presence of perchlorate counter anion. An intense band at�850 cm�1 confirms the presence of PF6

� counter anion for thecomplexes 2, 4, 6, 8 and 10 respectively.

Crystal structures

[Zn(N3)(dbdmp)]ClO4 (1)The ORTEP representation of the complex [Zn(N3)(dbdmp)]ClO4

is shown in Fig. 1. Selected bond length and bond angles are givenin Table 2. The structure of [Zn(N3)(dbdmp)]ClO4 consists of mono-meric [Zn(N3)(dbdmp)]+ cation and crystallized in monoclinic crys-tal system with centro symmetric space group P21/c. The liganddbdmp is tetradentate, utilized all the four potential N4-donor sitesN(1), N(3), N(5), N(6) for bonding in the complex. As shown inFig. 1, the zinc atom is five coordinated and the geometry aroundzinc(II) can be best described as distorted trigonal bipyramidal asindicated by the magnitude of the trigonality index s �0.835[s = (a � b)/60, where a and b are the two largest coordinationangles]. For the perfect square pyramidal and trigonal bipyramidalgeometries, the s-values are zero and unity, respectively [44]. Thezinc(II) ion is coordinated by five nitrogen donor atoms – fournitrogen atoms from ligand dbdmp and one nitrogen [N(7)] of ter-minal azide ion. In the basal plane, there are three nitrogen atomsN(1), N(5) and N(6) of ligand dbdmp and axial plane are occupiedby N(3) of dbdmp and N(7) of terminal azide ion. The bond lengthsare in the range of 2.0517(11) to 2.117(11) Å in the equatorialplane and axial bond ZnAN(3) (2.304(12) Å) is longer thanZnAN(7) 2.0001(13) (Å). The ZnAN(7) distance 2.0001(13) Å is

A. Solanki et al. / Journal of Molecular Structure 1076 (2014) 475–482 481

comparable with the corresponding distance (1.978–2.036 Å) givenfor other mononuclear five coordinated zinc(II) azido complex pre-viously reported [37–39]. The bond angle Zn(1)AN(7)AN(8) is129.71� but the bond angle (176.60�) of terminal azide ionN(7)AN(8)AN(9) is close to 180�. The axial bond angle is175.76(5)� but the equatorial bond angles are in the range of109.44(4)� to 125.71(4)�.

[{Cd(dbdmp)}2(l-N3)2](ClO4)2 (7)The molecular structure of the dimeric cationic moiety of com-

plex 7 is crystallized in monoclinic crystal system with centro sym-metric space group P21/c. Atom-lebeling scheme is shown in Fig. 2and selected bond lengths and angles for the metal coordinationsphere of the structure are given in Table 2. The structure showsthat the two azide ions bridges two cadmium(II) centers by adopt-ing end-to-end (l-1,3) coordination mode. The geometry aroundeach cadmium is distorted octahedral and each cadmium centeris blocked by three five membered chelate ring. The double end-to-end azide bridges link two symmetry related centers formingan eight-membered CdA(l1,3-N3)2ACd bridging ring and formschair conformation. The CdAN(7) bond (2.222(4) Å) is muchshorter than CdAN(8) bond (2.617(4) Å)) of azide ion which mightbe caused by azide ion-azide ion repulsion in the two CdN3 moie-ties. Each cadmium is bonded to four nitrogen atoms-two tertiarynitrogen atoms N(3) and N(6) from ligand and two nitrogen atoms(N(7), N(8)) from two azide ions in the equatorial position and thetwo pyrazole nitrogen atoms N(5) and N(1) at the axial position. Inthe basal plane, the bond lengths CdAN(6) (2.375 Å), CdAN(7)(2.221 Å), CdAN(8) (2.616 Å) and CdAN(3) (2.453 Å) are approxi-mately equal. The two axial lengths CdAN(5) (2.307(3) Å) andCdAN(1) (2.289 Å) are nearly equal. The bond anglesN(7)ACd(1)AN(3) is 172.15� and N(1)ACd(1)AN(5) is 138.46�. Thisis a dimeric structure and the bond length of Cd(1)AN(7) andCd(1i)AN(7i) are equal (2.221 Å). Since the distance betweenCdAN(8) (2.617(4) Å) is longer than CdAN(7) bond(2.222(4) Å), itcan be concluded that the interaction between Cd and N(8) of azideion is very weak. The bridging azide ions are quasilinear as isreflected in the N(7)AN(9)AN(8) bond angle 176.5(4)�. The Cd� � �Cddistance is 5.4701(4) Å which lie in the normal rang found forrelated end-to-end (l-1,3) azide bridged compounds [45].

[Cd(NCO)(dbdmp)]ClO4 (9)The ORTEP diagram of the complex [Cd(NCO)(dbdmp)]ClO4 is

shown in Fig. 3 and selected bond length and bond angles are givenin Table 2. The structure of [Cd(NCO)(dbdmp)]ClO4 consists ofmonomeric [Cd(NCO)(dbdmp)]+ cation and crystallized in mono-clinic crystal system with centro symmetric space group P21/c. Asshown in Fig. 3, the cadmium atom is five coordinated where fourcoordination sites are occupied by four nitrogen atom [N(1), N(3),N(5) and N(6)] of ligand dbdmp and one nitrogen [N(7)] of terminalNCO� ion. The geometry around cadmium(II) ion can be bestdescribed either as distorted trigonal bipyramidal or as distortedsquare pyramidal as indicated by the magnitude of the trigonalityindex s � 0.55. The equatorial plane is occupied by N(1), N(5) andN(6) atoms of ligand dbdmp and the two axial plane is occupied byN(3) of dbdmp and N(7) of terminal NCO� ion. The equatorial bondlengths are in the range of 2.290(6) Å to 2.351(7) Å and axial bondlengths are 2.157(7) Å and 2.445(7) Å. The CdAN(NCO) bondlength is comparable to other reported CdAN(NCO) bond length(2.329(2) Å) of polynuclear cadmium(II) isocyanate complex [46].The bond angle N3ACd1AN7 is 169.35� but the bond angle of ter-minal NCO� ion N(7)AC(19)AO(5) (178.60�) is close to 180�. Theaxial bond angle is 169.4(3)� and equatorial bond angles are inthe range of 96.3(4)� to 136.0(2)�.

[Cd(NCS)2(dbdmp)] (11)The ORTEP representation of the complex [Cd(NCS)2(dbdmp)]

(11) is shown in Fig. 4. Selected bond length and bond angles aregiven in Table 2. The structure of [Cd(NCS)2(dbdmp)] reveals thatcomplex 11 is a nonionic complex and crystallized in monocliniccrystal system with space group C2/c, where two NCS� ions areattached in cis position with respect to Cd(II) atom. The geometryaround Cd(II) ion is distorted octahedral with CdN6 coordinationenvironment ligated by four nitrogen atoms of ligand dbdmp[N(1), N(3), N(5) and N(6)] and two nitrogen of terminal thiocya-nate ions. The basal plane of complex consists of two tertiaryamines’ nitrogen atoms of dbdmp [N(3) and N(6)] and two nitro-gen atoms [N(7) and N(8)] of two terminal thiocyanate ions whilethe axial position is occupied by N(1) and N(5) nitrogen atoms ofpyrazole ring of dbdmp. The two axial bond lengths Cd(1)AN(1)and Cd(1)AN(5) are 2.369(3) and 2.357(3) Å, respectively and theequatorial bond lengths are in the range of 2.223(3)–2.540(3) Å.The equatorial bond angles N(7)ACd(1)AN(3) andN(8)ACd(1)AN(6) are 169.28(12)� and 163.59(13)�, respectivelywhereas the axial bond angle N(1)ACd(1)AN(5) is 143.17(11)�.The terminal N-donor thiocyanate ions are coordinated to Cd(II)center in almost linear fashion (�176�). The two CdAN(NCS) bonddistances are in the range of 2.223–2.540 Å and is comparable withcorresponding value (2.343 Å) given by other hexacoordinated NCScontaining Cd(II) complexes reported earlier [47–49]. The fourCdAN(dbdmp) bonds are in the range of 2.315–2.480 Å in all thethree cadmium (II) complexes 7, 9 and 11, but the CdAN(NCS)bondlengths (2.223(3) and 2.540(3) Å) are longer than CdAN(NCO)bond length 2.157(7) Å.

Conclusion

This paper describes the syntheses and characterization ofmononuclear zinc(II) complexes [Zn(X)(dbdmp)]Y (X = N3

�/NCO�/NCS� and Y = ClO4

�/PF6�), mononuclear cadmium(II) complexes

[Cd(NCS)2(dbdmp)] and [Cd(NCO)](dbdmp)]Y and binuclear azidebridged cadmium(II) complexes [{Cd(dbdmp)}2(l-N3)2](Y)2

(Y = PF6�/ClO4

�). The single crystal X-ray structure shows five coor-dinated cadmium(II) and zinc(II) complexes have distorted trigonalbipyramidal geometry with MN5 (M = Cd and Zn) coordinationenvironment, [Cd(NCS)2(dbdmp)] has octahedral geometry andthe geometry around each cadmium atom in binuclear azidebridged cadmium (II) complex [{Cd(dbdmp)}2(l-N3)2](ClO4)2 hasdistorted octahedral geometry. The prefered geometry for pyrazolecontaining N4-coordinating tetradentate ligand is either trigonalbipyramidal or distorted octahedral for zinc(II) and cadmium(II)complexes in presence of N3

�/NCS�/NCO� ions and binuclear azidebridged cadmium(II) complex has end-to-end (l-1,3) bridgingcoordination mode.

Acknowledgements

Financial support from UGC-India in the form of major researchproject (F.No. 39-720/2010(SR)) is gratefully acknowledged. A.Solanki thanks UGC for BSR fellowship. The authors acknowledgethe use of DST-funded National Single Crystal X-ray diffractionfacility at the Department of Inorganic Chemistry, IACS, Kolkataand DST-Purse program at Faculty of Science, The M.S. Universityof Baroda and Dr. R, Rathore for helpful discussion. We would liketo thank reviewers and Associate editor for valuable suggestions.

Appendix A. Supplementary material

CCDC 932054, 890814, 957335 and 890813contain the supple-mentary crystallographic data for 1, 9 and 11. This data can be

482 A. Solanki et al. / Journal of Molecular Structure 1076 (2014) 475–482

obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Cen-ter, 12 Union Road, Cambridge CB12 1EW, UK (fax: +44 1223 336033; e. mail: deposit@ccdc.cam.ac.uk. Supplementary data associ-ated with this article can be found, in the online version, athttp://dx.doi.org/10.1016/j.molstruc.2014.07.082.

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